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linux-next/drivers/xen/evtchn.c
Daniel De Graaf 420eb554d5 xen/event: Add reference counting to event channels 
Event channels exposed to userspace by the evtchn module may be used by
other modules in an asynchronous manner, which requires that reference
counting be used to prevent the event channel from being closed before
the signals are delivered.

The reference count on new event channels defaults to -1 which indicates
the event channel is not referenced outside the kernel; evtchn_get fails
if called on such an event channel. The event channels made visible to
userspace by evtchn have a normal reference count.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-11-21 17:14:48 -05:00

561 lines
13 KiB
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/******************************************************************************
* evtchn.c
*
* Driver for receiving and demuxing event-channel signals.
*
* Copyright (c) 2004-2005, K A Fraser
* Multi-process extensions Copyright (c) 2004, Steven Smith
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation; or, when distributed
* separately from the Linux kernel or incorporated into other
* software packages, subject to the following license:
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this source file (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/major.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <linux/init.h>
#include <linux/mutex.h>
#include <linux/cpu.h>
#include <xen/xen.h>
#include <xen/events.h>
#include <xen/evtchn.h>
#include <asm/xen/hypervisor.h>
struct per_user_data {
struct mutex bind_mutex; /* serialize bind/unbind operations */
/* Notification ring, accessed via /dev/xen/evtchn. */
#define EVTCHN_RING_SIZE (PAGE_SIZE / sizeof(evtchn_port_t))
#define EVTCHN_RING_MASK(_i) ((_i)&(EVTCHN_RING_SIZE-1))
evtchn_port_t *ring;
unsigned int ring_cons, ring_prod, ring_overflow;
struct mutex ring_cons_mutex; /* protect against concurrent readers */
/* Processes wait on this queue when ring is empty. */
wait_queue_head_t evtchn_wait;
struct fasync_struct *evtchn_async_queue;
const char *name;
};
/*
* Who's bound to each port? This is logically an array of struct
* per_user_data *, but we encode the current enabled-state in bit 0.
*/
static unsigned long *port_user;
static DEFINE_SPINLOCK(port_user_lock); /* protects port_user[] and ring_prod */
static inline struct per_user_data *get_port_user(unsigned port)
{
return (struct per_user_data *)(port_user[port] & ~1);
}
static inline void set_port_user(unsigned port, struct per_user_data *u)
{
port_user[port] = (unsigned long)u;
}
static inline bool get_port_enabled(unsigned port)
{
return port_user[port] & 1;
}
static inline void set_port_enabled(unsigned port, bool enabled)
{
if (enabled)
port_user[port] |= 1;
else
port_user[port] &= ~1;
}
static irqreturn_t evtchn_interrupt(int irq, void *data)
{
unsigned int port = (unsigned long)data;
struct per_user_data *u;
spin_lock(&port_user_lock);
u = get_port_user(port);
WARN(!get_port_enabled(port),
"Interrupt for port %d, but apparently not enabled; per-user %p\n",
port, u);
disable_irq_nosync(irq);
set_port_enabled(port, false);
if ((u->ring_prod - u->ring_cons) < EVTCHN_RING_SIZE) {
u->ring[EVTCHN_RING_MASK(u->ring_prod)] = port;
wmb(); /* Ensure ring contents visible */
if (u->ring_cons == u->ring_prod++) {
wake_up_interruptible(&u->evtchn_wait);
kill_fasync(&u->evtchn_async_queue,
SIGIO, POLL_IN);
}
} else
u->ring_overflow = 1;
spin_unlock(&port_user_lock);
return IRQ_HANDLED;
}
static ssize_t evtchn_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
int rc;
unsigned int c, p, bytes1 = 0, bytes2 = 0;
struct per_user_data *u = file->private_data;
/* Whole number of ports. */
count &= ~(sizeof(evtchn_port_t)-1);
if (count == 0)
return 0;
if (count > PAGE_SIZE)
count = PAGE_SIZE;
for (;;) {
mutex_lock(&u->ring_cons_mutex);
rc = -EFBIG;
if (u->ring_overflow)
goto unlock_out;
c = u->ring_cons;
p = u->ring_prod;
if (c != p)
break;
mutex_unlock(&u->ring_cons_mutex);
if (file->f_flags & O_NONBLOCK)
return -EAGAIN;
rc = wait_event_interruptible(u->evtchn_wait,
u->ring_cons != u->ring_prod);
if (rc)
return rc;
}
/* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
if (((c ^ p) & EVTCHN_RING_SIZE) != 0) {
bytes1 = (EVTCHN_RING_SIZE - EVTCHN_RING_MASK(c)) *
sizeof(evtchn_port_t);
bytes2 = EVTCHN_RING_MASK(p) * sizeof(evtchn_port_t);
} else {
bytes1 = (p - c) * sizeof(evtchn_port_t);
bytes2 = 0;
}
/* Truncate chunks according to caller's maximum byte count. */
if (bytes1 > count) {
bytes1 = count;
bytes2 = 0;
} else if ((bytes1 + bytes2) > count) {
bytes2 = count - bytes1;
}
rc = -EFAULT;
rmb(); /* Ensure that we see the port before we copy it. */
if (copy_to_user(buf, &u->ring[EVTCHN_RING_MASK(c)], bytes1) ||
((bytes2 != 0) &&
copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
goto unlock_out;
u->ring_cons += (bytes1 + bytes2) / sizeof(evtchn_port_t);
rc = bytes1 + bytes2;
unlock_out:
mutex_unlock(&u->ring_cons_mutex);
return rc;
}
static ssize_t evtchn_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
int rc, i;
evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
struct per_user_data *u = file->private_data;
if (kbuf == NULL)
return -ENOMEM;
/* Whole number of ports. */
count &= ~(sizeof(evtchn_port_t)-1);
rc = 0;
if (count == 0)
goto out;
if (count > PAGE_SIZE)
count = PAGE_SIZE;
rc = -EFAULT;
if (copy_from_user(kbuf, buf, count) != 0)
goto out;
spin_lock_irq(&port_user_lock);
for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
unsigned port = kbuf[i];
if (port < NR_EVENT_CHANNELS &&
get_port_user(port) == u &&
!get_port_enabled(port)) {
set_port_enabled(port, true);
enable_irq(irq_from_evtchn(port));
}
}
spin_unlock_irq(&port_user_lock);
rc = count;
out:
free_page((unsigned long)kbuf);
return rc;
}
static int evtchn_bind_to_user(struct per_user_data *u, int port)
{
int rc = 0;
/*
* Ports are never reused, so every caller should pass in a
* unique port.
*
* (Locking not necessary because we haven't registered the
* interrupt handler yet, and our caller has already
* serialized bind operations.)
*/
BUG_ON(get_port_user(port) != NULL);
set_port_user(port, u);
set_port_enabled(port, true); /* start enabled */
rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
u->name, (void *)(unsigned long)port);
if (rc >= 0)
rc = evtchn_make_refcounted(port);
return rc;
}
static void evtchn_unbind_from_user(struct per_user_data *u, int port)
{
int irq = irq_from_evtchn(port);
unbind_from_irqhandler(irq, (void *)(unsigned long)port);
set_port_user(port, NULL);
}
static long evtchn_ioctl(struct file *file,
unsigned int cmd, unsigned long arg)
{
int rc;
struct per_user_data *u = file->private_data;
void __user *uarg = (void __user *) arg;
/* Prevent bind from racing with unbind */
mutex_lock(&u->bind_mutex);
switch (cmd) {
case IOCTL_EVTCHN_BIND_VIRQ: {
struct ioctl_evtchn_bind_virq bind;
struct evtchn_bind_virq bind_virq;
rc = -EFAULT;
if (copy_from_user(&bind, uarg, sizeof(bind)))
break;
bind_virq.virq = bind.virq;
bind_virq.vcpu = 0;
rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
&bind_virq);
if (rc != 0)
break;
rc = evtchn_bind_to_user(u, bind_virq.port);
if (rc == 0)
rc = bind_virq.port;
break;
}
case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
struct ioctl_evtchn_bind_interdomain bind;
struct evtchn_bind_interdomain bind_interdomain;
rc = -EFAULT;
if (copy_from_user(&bind, uarg, sizeof(bind)))
break;
bind_interdomain.remote_dom = bind.remote_domain;
bind_interdomain.remote_port = bind.remote_port;
rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
&bind_interdomain);
if (rc != 0)
break;
rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
if (rc == 0)
rc = bind_interdomain.local_port;
break;
}
case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
struct ioctl_evtchn_bind_unbound_port bind;
struct evtchn_alloc_unbound alloc_unbound;
rc = -EFAULT;
if (copy_from_user(&bind, uarg, sizeof(bind)))
break;
alloc_unbound.dom = DOMID_SELF;
alloc_unbound.remote_dom = bind.remote_domain;
rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
&alloc_unbound);
if (rc != 0)
break;
rc = evtchn_bind_to_user(u, alloc_unbound.port);
if (rc == 0)
rc = alloc_unbound.port;
break;
}
case IOCTL_EVTCHN_UNBIND: {
struct ioctl_evtchn_unbind unbind;
rc = -EFAULT;
if (copy_from_user(&unbind, uarg, sizeof(unbind)))
break;
rc = -EINVAL;
if (unbind.port >= NR_EVENT_CHANNELS)
break;
spin_lock_irq(&port_user_lock);
rc = -ENOTCONN;
if (get_port_user(unbind.port) != u) {
spin_unlock_irq(&port_user_lock);
break;
}
disable_irq(irq_from_evtchn(unbind.port));
spin_unlock_irq(&port_user_lock);
evtchn_unbind_from_user(u, unbind.port);
rc = 0;
break;
}
case IOCTL_EVTCHN_NOTIFY: {
struct ioctl_evtchn_notify notify;
rc = -EFAULT;
if (copy_from_user(&notify, uarg, sizeof(notify)))
break;
if (notify.port >= NR_EVENT_CHANNELS) {
rc = -EINVAL;
} else if (get_port_user(notify.port) != u) {
rc = -ENOTCONN;
} else {
notify_remote_via_evtchn(notify.port);
rc = 0;
}
break;
}
case IOCTL_EVTCHN_RESET: {
/* Initialise the ring to empty. Clear errors. */
mutex_lock(&u->ring_cons_mutex);
spin_lock_irq(&port_user_lock);
u->ring_cons = u->ring_prod = u->ring_overflow = 0;
spin_unlock_irq(&port_user_lock);
mutex_unlock(&u->ring_cons_mutex);
rc = 0;
break;
}
default:
rc = -ENOSYS;
break;
}
mutex_unlock(&u->bind_mutex);
return rc;
}
static unsigned int evtchn_poll(struct file *file, poll_table *wait)
{
unsigned int mask = POLLOUT | POLLWRNORM;
struct per_user_data *u = file->private_data;
poll_wait(file, &u->evtchn_wait, wait);
if (u->ring_cons != u->ring_prod)
mask |= POLLIN | POLLRDNORM;
if (u->ring_overflow)
mask = POLLERR;
return mask;
}
static int evtchn_fasync(int fd, struct file *filp, int on)
{
struct per_user_data *u = filp->private_data;
return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
}
static int evtchn_open(struct inode *inode, struct file *filp)
{
struct per_user_data *u;
u = kzalloc(sizeof(*u), GFP_KERNEL);
if (u == NULL)
return -ENOMEM;
u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
if (u->name == NULL) {
kfree(u);
return -ENOMEM;
}
init_waitqueue_head(&u->evtchn_wait);
u->ring = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
if (u->ring == NULL) {
kfree(u->name);
kfree(u);
return -ENOMEM;
}
mutex_init(&u->bind_mutex);
mutex_init(&u->ring_cons_mutex);
filp->private_data = u;
return nonseekable_open(inode, filp);
}
static int evtchn_release(struct inode *inode, struct file *filp)
{
int i;
struct per_user_data *u = filp->private_data;
spin_lock_irq(&port_user_lock);
free_page((unsigned long)u->ring);
for (i = 0; i < NR_EVENT_CHANNELS; i++) {
if (get_port_user(i) != u)
continue;
disable_irq(irq_from_evtchn(i));
}
spin_unlock_irq(&port_user_lock);
for (i = 0; i < NR_EVENT_CHANNELS; i++) {
if (get_port_user(i) != u)
continue;
evtchn_unbind_from_user(get_port_user(i), i);
}
kfree(u->name);
kfree(u);
return 0;
}
static const struct file_operations evtchn_fops = {
.owner = THIS_MODULE,
.read = evtchn_read,
.write = evtchn_write,
.unlocked_ioctl = evtchn_ioctl,
.poll = evtchn_poll,
.fasync = evtchn_fasync,
.open = evtchn_open,
.release = evtchn_release,
.llseek = no_llseek,
};
static struct miscdevice evtchn_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "xen/evtchn",
.fops = &evtchn_fops,
};
static int __init evtchn_init(void)
{
int err;
if (!xen_domain())
return -ENODEV;
port_user = kcalloc(NR_EVENT_CHANNELS, sizeof(*port_user), GFP_KERNEL);
if (port_user == NULL)
return -ENOMEM;
spin_lock_init(&port_user_lock);
/* Create '/dev/misc/evtchn'. */
err = misc_register(&evtchn_miscdev);
if (err != 0) {
printk(KERN_ALERT "Could not register /dev/misc/evtchn\n");
return err;
}
printk(KERN_INFO "Event-channel device installed.\n");
return 0;
}
static void __exit evtchn_cleanup(void)
{
kfree(port_user);
port_user = NULL;
misc_deregister(&evtchn_miscdev);
}
module_init(evtchn_init);
module_exit(evtchn_cleanup);
MODULE_LICENSE("GPL");
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